. People are building rear seats for GEMs using only the attachment lock. This is only rated for 100 pounds. The document below is my installation instructions for a SAFE rear seat. You can build from the pictures in this paper. I use an EZGO seat and 1 !/4 inch square tubing. Attachments are 1/2 threaded rod with (4) 1/2 inch nuts each side. Please copy and post to other forums to help avoid accidents.
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MOUNTING INSTRUCTIONS FOR GEM CAR REAR SEAT